In current day processing equipment handling hot and abrasive material, such as biomass boiler and feeder systems, wear of valves and pipes in the system is a common problem. In particular, problems of wear as well as plugging is common when hot (or cold) blowing material out of a pressurized processing container for further transportation in a pipe system. This causes severe costs and contributes to time loss due to maintenance, repair and replacement of wear parts such as valves and couplings. In the following description the terminology hot and cold blowing will be used. For cold blowing the material to be processed has been cooled down below 100° C. by adding water e.g. the concentration is low and thereby the material leaving the outlet is less abrasive. Hot blow or steam explosion implies that the material is both warmer and less diluted, thus causing a more abrasive wear on the processing equipment.
One known valve utilized in such systems is a so called gate-valve, in which flow is controlled by lowering or raising a gate like valve. When processing non-homogeneous material in which there is a size distribution of the particles in the material, a gate valve is very likely to trap larger particles of the material due to plugging whilst smaller particles manage to escape through the remaining opening “beneath” the gate.
Another know valve utilized in such systems is a so called ball valve, in which flow is controlled by rotating a ball with a central perforation. During such a rotation the flow of material is no longer centralized in the pipe in which the valve is located, but rather sprays across the pipe during closing or opening of the valve. When handling abrasive and optionally hot material this might cause severe wear and possible puncture of nearby walls of the pipe.
Therefore, there is a need for control of the outlet flow which overcomes the above described disadvantages.